Vanadium base alloys containing niobium and titanium

ABSTRACT

ALLOYS COMPOSED OF 12-25%, PREFERABLY, 14-16% OF NIOBIUM, 1 TO LESS THAN 3%, PREFERABLY, 2.6-2.9%, OF TITANIUM, UP TO 1/2 OF THE TITANIUM BEING REPLACEABLE WITH ZIRCONIUM AND/OR HAFNIUM, NOT MORE THAN 1% OF CARBON, NITROGEN AND OXYGEN, UP TO 1.5% OF SILICON AND THE REMAINDER VANADIUM, SAID ALLOYS HAVING HIGH CORROSION RESISTANCE REMAINING STABLE OVER LONG PERIODS OF TIME AT TEMPERATURE BETWEEN 500 AND 800*C. AND HAVING UTILITY AS CONSTRUCTION MATERIALS IN NUCLEAR REACTORS, ESPECIALLY THOSE HAVING COOLING SYSTEMS USING MOLTEN ALKALI METALS, SPACE VEHICLES AND CHEMICAL APPARATUS.

y 4, 1972 HANSJURGEN R. LAUE ErAL 3,674,470

VANADIUM BASE ALLOYS CONTAINING NIOBIUM AND TITANIUM Filed Aug. 8, 1968 2 Sheets-Sheet l \igl xaw W) aao y 4, 1972 ANS-JURGEN R. LAUE ETAL 3,674,470

VANADIUM BASE ALLOYS CONTAINING NIOBIUM AND TITANIUM Filed Aug. 8, 1968 2 Sheets-Sheet 2 LIFE 4 040 60 kg/m 7?? 0 g A/&

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United States Patent 3,674,470 VANADIUM BASE ALLOYS CONTAINING NIOBIUM AND TITANIUM Hans-lurgen Rainer Laue and Horst Otto Bohm, Karlsruhe, and Bernhard Hermann Reddemann, Werdohl- Barenstein, Germany, amignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Filed Aug. 8, 1968, Ser. No. 751,242 Int. Cl. C22c 27/00 US. Cl. 75-134 V 7 Claims ABSTRACT OF THE DISCLOSURE Alloys composed of 1-225%, preferably, 14-16% of niobium, 1 to less than 3%, preferably, 26-29%, of titanium, up to /2 of the titanium being replaceable with zirconium and/or hafnium, not more than 1% of carbon, nitrogen and oxygen, up to 1.5% of silicon and the remainder vanadium, said alloys having high corrosion resistance remaining stable over long periods of time at temperatures between 500 and 800 C. and having utility as construction materials in nuclear reactors, especially those having cooling systems using molten alkali metals, soace vehicles and chemical apparatus.

BACKGROUND OF THE INVENTION Vanadium based alloys are known which essentially consist of 15-60% of niobium, 325% of titanium and the remainder vanadium (Canadian Pat. No. 716,521). In view of their mechanical properties at elevated temperatures and their good corrosion resistance in aqueous and gaseous media they were proposed as construction material for the propulsion systems for air and space travel or for nuclear reactors.

Furthermore, vanadium'alloys containing 06-10% of niobium and 25-15% of titanium have been suggested for the same purposes (US. Pat. No. 2,886,431). It also is known that va'nadium base alloys with a high niobium content are stable for reasonable periods of time, but possess a very high capture cross-section for high velocity neutrons. 0n the other hand, vanadium base alloys with a low niobium content have a more favorable absorption cross-section for high velocity neutrons but their lack of stability over long periods of time is extremely disadvantageous for many applications in the construction of nuclear reactors. This inadequate stability requires use of according to the invention consist of 12-25% of niobium, 1 to less than 3% titanium, up to /2 of the titanium being replaceable by zirconium and/or hafnium, not more than 1% as a whole of carbon, nitrogen and oxygen, up to 1.5% of silicon and the remainder vanadium.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 graphically shows the increase in stability (creep resistance) of vanadium-niobium-titanium alloys with low titanium content; and

FIG. 2 graphically shows the influence of the niobium content on the stability of an alloy according to the invention and of a known alloy containing 5% of titanium.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS The vanadium base alloys according to the invention essentially consist of 12-25% of niobium, 1 to less than 3 of titanium, up to /2 of the titanium being replaceable by zirconium and/or hafnium, not more than 1% as a whole of carbon, nitrogen and oxygen, if desired, up to 1.5 of silicon and the remainder vanadium. In the above and in the following the proportions are given by weight.

An alloy which has been particularly suited to the requirements of the practice essentially consists of:

14-16% of niobium 26-29% of titanium 500-4000 p.p.m. of carbon, nitrogen and oxygen remainder vanadium Such an alloy with 14.5% of niobium and 2.8% of titanium has an unexpectedly high stability over long periods of time with a life of about 1250 hours under a load of 50 kg./mm. at 650 C. which is superior to any known niobium and titanium containing vanadium based alloys as well as stainless steel. This unexpectedly good stability is achieved with a relatively low niobium content so that the alloy according to the invention in view of its high stability renders a favorable neutron economy larger cross-sections and therefore again a reduction in the neutron economy.

In addition, it is known that the stability of vanadium base alloys which do not contain niobium or titanium over long periods of time can be increased by the addition of silicon as a hardening agent. In such alloys a useful life of 60 hours under a tensile stress of kg./mm. at 650 C. has been considered the maximum. A disadvantage of such silicon hardened alloys is their very low ductility.

SUMMARY OF THE INVENTION possible.

It was furthermore found that the additions of titanium within the indicated range improve the properties of the vanadium base alloys considerably and that good ductility and deformability is achieved and retained in the alloys according to the invention without the alloy having a tendency to high temperature embrittlement When subjected to neutron irradiation. In addition, the titanium content according to the invention leads to high corrosion resistance to molten alkali metals, the resistance increasing with lowering of the titanium content.

The carbon, nitrogen and oxygen content together with the titanium content of the alloys according to the invention serves to improve the mechanical properties of the alloys, utilizing the known scavenger efiect.

An addition of up to 1.5% of silicon causes a further increase in the strength of the alloys according to the invention. Generally, additions of (LS-1% suflice to effect a noticeable increase. For example, alloys of the following composition have favorable properties:

14-16% of niobium 2.6-2.9% of titanium (1.5-1% of silicon 500-4000 p.p.m. of carbon, nitrogen and oxygen remainder vanadium In such instances where an additional improvement in ductility is desired, it is advantageous to replace up to /2 of the titanium content of the alloys according to the invention with zirconium and/or hafnium. The following for instance, is an example of an alloy of this type:

14-16% of niobium 1.5-2.5% of titanium 0.4 to less than 1.5% of zirconium 500-4000 p.p.m. of carbon, nitrogen and oxygen remainder vanadium As can be seen from FIG. 1 of the accompanying drawings where the stability of vanadium-% niobium, titanium and vanadium-15% niobium, titanium alloys with varying titanium content is graphically shown, those alloys containing less than 3% of titanium have an extraordinarily increased stability. FIG. 2, on the other hand, shows the substantially increased stability achieved in the alloys according to the invention with 2.8% of titanium as contrasted to a V-Nb-Ti alloy containing 5% of Ti.

The excellent properties of the alloys according to the invention, especially their high stability over long periods of time (creep resistance), their small neutron capture cross-section their high corrosion resistance against molten alkali metals, as well as their good deformability, are decisive prerequisites for their use as casing material for fuel elements and other structural parts of nuclear reactors. The alloys according to the invention are materials having superior properties and they can be used with particular advantage as materials for the construction of parts which must have high stability at temperatures between 500 and 800 C. and at the same time corrosion resistance against molten alkali metals, especially, sodium, and in addition a low tendency to embrittlement when irradiated with neutrons or any one of such properties.

The above indicated properties of the alloys according to the invention are especially noticeable in shaped parts produced therefrom under vacuum or an inert atmosphere such as argon or helium.

The alloys according to the invention are especially suited for the construction of structural elements or shaped parts for nuclear reactors and particularly for the construction of casings for fuel elements of nuclear reactors using high velocity neutrons. In addition, the

excellent corrosion resistance of the alloys according to the invention renders them useful for the production of chemical apparatus and their high heat resistance renders them suitable as materials employed in space travel.

The alloys according to the invention can be produced by generally known metallurgical processes, such as, for example, melting under vacuum or an inert atmosphere or by sintering in powder metallurgical processes. Such alloys are readily processed to shaped parts by rolling, extrusion or drawing.

We claim:

1. A vanadium base alloy consisting essentially of 12- wt. percent of niobium, 1 to less than 3 wt. percent of a component selected from the group consisting of first titanium and secondly titanium and at least one of zirconium and hafnium, with the zirconium and hafnium at most replacing of the permissible 1 to less than 3% titanium content, a total of from about 500 p.p.m.. to not more than 1 wt. percent of carbon, nitrogen and oxygen, 0 to 1.5 wt. percent of silicon and the remainder vanadium.

2. A vanadium base alloy according to claim 1 which consists essentially of 14-16 wt. percent of niobium, 2.6- 2.9 wt. percent of titanium, a total of 500-4000 p.p.m. of carbon, nitrogen and oxygen and the remainder vanadium.

3. A vanadiumbase alloy according to claim 1 which consists essentially of 14-16 wt. percent of niobium, 2.6- 2.9 wt. percent of titanium, 0.5-1 wt. percent of silicon, a total of 500-4000 p.p.m. of -carbon,-nitrogen and oxygen and the remainder vanadium.

4. A vanadium base alloy according to claim 1 which consists essentially of 14-16 wt. percent of niobium, 1.5-2.5 wt. percent of titanium, 0.4-1.5 wt. percent of zirconium, a total of 500-4000 p.p.m. of carbon, nitrogen and oxygen and the remainder vanadium.

5. A nuclear reactor part comprising a body composed of a vanadium base alloy consisting essentially of 12-25 wt. percent of niobium, 1 to less than 3 wt. percent of a component selected from the group consisting of first titanium and secondly titanium and at least one of zirconium and hafnium, with the zirconium and hafnium at most replacing /2 of the permissible l to less than 3% titanium content, a total of from about SSO p.p.m. to not more than 1 wt. percent of carbon, nitrogen: and oxygen, 0 to 1.5 wt. percent of silicon and the remainder vanadium.

6. A space vehicle structural part comprising a body composed of a vanadiumbase alloy consisting essentially of 12-25 wt. percent of niobium,.1 to less than 3 wt. percent of a component selected from the group consisting of first titanium and secondly titanium and at least one of zirconium and hafnium, with the zirconium and hafnium at most replacing of the permissiblel to less than 3% titanium content, a total of from about 500 p.p.m. to not more than 1 wt. percent of carbon, nitrogen and oxygen, 0 to 1.5 wt. percent of silicon and the remainder vanadium. I

7. A nuclear fuel element casing comprising a body composed of a vanadium base alloy consisting essentially of 12- 25 .wt. percent of niobium, 1 to less than 3 wt. percent of a component selected from the group consisting of first titanium and'secondly .titaniumand at least oneof zirconium and hafnium, with the zirconium and hafnium at most replacing /z of the permissible 1 to less than 3% titanium content, a total of from about 500 p.p.m. to not more than 1 wt. percent of carbon, nitrogen and oxygen, 0 to 1.5 wt. percent of silicon and the rea mainder vanadium.

References Cited UNITED STATES PATENTS OTHER REFERENCES Improved Vanadium-Base Alloys, Final Report, ARF 2191-6 (Armour Research Foundation to Department of the Navy), Dec. 27, 1960, page 4 relied on.

-L.. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner 

